1. Field of the Invention
The present invention concerns a wire wound electronic part used, for example, in mobile electronic equipments or thin electronic equipments.
2. Description of the Related Technology
Wire wound type electronic parts are used as step up circuit coils for DC/DC power sources in cellular phones or mobile electronic equipments such as digital still cameras and choke coils in peripheral circuits of various kinds of flat panel displays. For the application uses described above, it is particularly demanded for those having a small and low-profile dimension capable of high density mounting or low-profile mounting while ensuring desired inductor characteristics.
Japanese Unexamined Patent Publication No. 2007-214521 discloses an example of a wire wound electronic part, a wire wound electronic part has, for example, a ferrite core, a pair of terminal electrodes disposed to the ferrite core and a coil conductor wound around the ferrite core and connected at the ends thereof to the terminal electrodes. The ferrite core includes a wire wound core, an upper flange disposed to the upper end of the wire wound core and a lower flange disposed to the lower end of the wire wound ferrite core. A pair of the terminal electrodes are formed on the bottom of the lower flange of the ferrite core. The terminal electrode is formed by coating an electrode paste mainly comprising Ag to the bottom of the lower flange of the ferrite core and then applying a heat treatment to the ferrite core, for example, in atmospheric air at 650° C., and has an Ag conduction layer. Further, in the terminal electrode, an Ni plating layer and a solder plating (Sn plating) layer are formed, for example, on the surface of the Ag conduction layer. The coil conductor comprises a metal wire having an insulation coating formed at the outer circumference thereof and is wound around the periphery of the wire wound core of the ferrite core. Then, one and the other ends of the coil conductor are removed with the insulation coating and connected to the terminal electrodes in which a plating layer is formed respectively by soldering.
FIG. 6 and FIG. 7 are views showing an example of the wire wound electronic part. FIG. 6 is a vertical cross sectional view taken along a central axis of a wire wound core 111a showing the inner structure of the wire wound electronic part 110. FIG. 7 is a perspective view for the appearance of a lower flange 111c of a ferrite core 111 used for the wire wound electronic part 110 as viewed on the side of the bottom 111B.
As shown in FIG. 6, it specifically discloses a wire wound electronic part 110 including the ferrite core 111 having a columnar wire wound the ferrite core 111a and flanges 111b, 111c formed at upper and lower ends thereof a coil conductor 112 wound around the wire wound core 111a of the ferrite core 111, and terminal electrodes 116A, 116B disposed at a bottom 111B crossing the wire wound core 111a of the flange 111c, in which both ends 113A, 113B of the coil conductor 112 wound around the wire wound core 111a are conductively connected to the terminal electrodes 116A, 116B by using solders 117, 117.
Then, as shown in FIG. 7, a pair of grooves 115, 115 are formed to the bottom 111B of the flange 111c of the ferrite core 111, and the groove 115 has a bottom 115a, and moderate slopes 115b, 115b disposed on both lateral sides of the bottom 115a being slanted to the bottom 115a. Then, the terminal electrodes 116A and 116B are formed so as to extend from a position above one moderate slope 115b of the groove 115 by way of the bottom 115a of the groove 115 to a position above the other moderate slope 115b. 
Then, the terminal electrodes 116A, 116B have, as shown in FIG. 6, an Ag conduction layer 116a formed by coating the electrode paste mainly comprising Ag to the bottom of the lower flange 111c of the ferrite core 111 and then applying a heat treatment to the ferrite core 111, for example, in atmospheric air, and an Ni plating layer 116b and an Sn plating layer 116c formed on the surface of the Ag conduction layer 116a. 
Further, Japanese Unexamined Patent Publication No. Hei 3-106005 proposes to adopt a Cu conduction layer instead of the existent Ag conduction layer in a composite electronic part in the application use different from the existent wire wound electronic part.
Specifically, it proposes a method of manufacturing a chip type LR filter by baking a core in air or an oxygen atmosphere, coating a conductive paste mainly comprising silver, silver-palladium, or copper to the outer surface of a flange of the baked core to form a pair of lead wire extending electrodes, and then baking the core in a reducing atmosphere such as H2 or CO gas, or in a neutral atmosphere such as an N2 or Ar gas at an oxygen concentration of 0.1% or less, thereby forming the lead extending electrode to the core and lowering the resistance of the core and, further, applying winding to a wire wound portion.
In the existent wire wound electronic part, when the thickness of the flange is decreased for lower-profile of the ferrite core, this brings about a possibility of generating flange fracture upon forming the Ni plating layer and the Sn plating layer on the Ag conduction layer.
For saving the plating layer, use of an Ag—Pd conduction layer or a Cu conduction layer instead of the Ag conduction layer is prospective.
However, as described in JP-A No. Hei 3-106005, in a case, for example, of coating a conductive paste mainly comprising copper to the outer surface of the flange of the core to form a pair of lead wire extending electrodes, then baking the core in a reducing atmosphere such as an H2 or Co gas or in a neutral atmosphere such as N2 or Ar gas at an oxygen concentration of 0.1% or less thereby forming the lead extending electrode to the core and lowering the resistance of the core, insulation performance between a pair of terminal electrode is lowered. Accordingly, this results in a problem that they cannot be used in a choke coil or the like for a power source used for certain commercial applications.